Technical Field
The present invention relates to a serial communication system.
Background Art
Many serial interface specifications have been practically used use to transmit a massive amount of data at a high speed.
For example, bidirectional communications are made between such as a camera and a controller and a display and a controller via a serial transmission line in a mobile phone. In this kind of bidirectional communications, for example, a massive amount of data such as image data are transmitted in the forward direction, and a relatively small quantity of data such as a control signal for controlling a circuit to transmit data in the forward direction are transmitted in the backward direction.
As the bidirectional communications, a full-duplex system to conduct concurrent communications in real time and a half-duplex system to conduct communications mutually in time-sharing. In the full-duplex system, multiple channels are utilized and signal lines only for the backward direction are provided. For this reason, more number of signal lines are required when compared with the half-duplex system. The half-duplex system is advantageous in terms of cost unless quick bidirectional communications are necessary.
As low speed full-duplex system communications, universal asynchronous receiver transmitter (UART) is already known.
For example, universal asynchronous serial data transmitters and receivers are introduced. The transmitter modulates single bit data to two bit data having different logical values and the receiver conducts reception synchronous to bit data by detecting the changing point of the logical values. This makes it possible to avoid errors ascribable to the difference between the clock frequency number of the transmitter and the clock frequency number of the receiver.
However, in conventional low speed asynchronous communication method, sufficiently precise clock signals are required in both a transmitter and a receiver.